Cool Roofs Would Save Los Angeles 83 Million Gallons of Water per day

As a product of their energy and temperature saving advantages, cool roofing also has water-saving properties according to new research.

In warm climates, especially during summertime, you may have noticed that light-colored clothes keep you cooler while dark-colored clothes attract tons of heat. This is because lighter colors reflect sunlight while darker colors absorb it.

The same goes for roofs. Conventional, dark roofs absorb sunlight and trap more heat in the roof itself and also the ambient air. This rise in temperature causes plants in the area to require more water; the house itself becomes warmer and more energy is spent cooling it from the inside with air conditioning.

A solution to this rise in temperature and energy consumption is installing a “cool roof”, or a roof that is lightly colored and able to reflect light and heat back up towards the sun.

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Responsible for about 25% of heat loss, roofs are one of the major points of thermal leakage of a building. The remaining heat travels through walls, windows, doors, and the floor.

Cool roofing is a green technique used to reduce the overheating of roofs thanks to the installation of materials with high solar reflectance and high thermal emittance, such as light-colored tarps, white foam coatings, and etc.

Cool roofs reflect more solar radiation into the atmosphere, and as the roof remains cooler, the amount of heat transmitted into the building is decreased, thus maintaining a cooler and more consistent indoor temperature, and less air-conditioning expenses.

Insulation slows down the external heat from reaching into the inside but it isn’t enough when it comes to saving energy during long, hot, sunny summer days. Just as an idea, studies estimate cool roofed buildings could save up to 10-15% on energy bills.

Compared to a conventional roof that could be up to 50°F hotter than the inside of the building, a cool roof might be only 5 to 10 degrees hotter.

This could have great positive impact on the environment by mitigating the effect of what’s known as an “urban heat island”. A UHI is a phenomenon induced by human activities in dense urban areas where there’s more warmth than in surrounding rural areas primarily due to heat absorbing materials, heat producing machinery, and overall urban density.

Cool-Colored Roofs cut Water Consumption

Because 90% of buildings in the U.S. have dark, heat-absorbing roofs, new research has shed light on another benefit of cool roofs that could push toward their adoption by companies and homeowners alike.

Researchers at the DoE’s Berkeley Lab conducted a study that revealed the water-saving benefit of cool roofs, primarily due to the cutting of urban irrigation water needs.

The Berkeley Lab research team, led by Pouya Vahmani and Andrew Jones, ran simulation models of 18 counties in Northern and Southern California over 15 years, and found that wide adoption of cool roofs could cut outdoor water demand by up to 9%.

Had all its roofs been switched to cool roofs, Los Angeles County alone could save up to 83 million gallons per day (9.1%), the highest rate among the 18 counties studied.

According to the study published in the journal Nature Communications, cool roofs reduce urban temperature by 1 to 1.5 degrees Celsius, which means less water needed for outdoor irrigation and landscaping.

“First we want to see how much climate change will increase water demand. Next will be to come up with strategies to counter that,” said researchers.

“In urban areas, we’ll look at how cool roofs can ameliorate both extreme heat demand and irrigation demands associated with future warming. Whereas in agricultural areas, the strategies will have to do with irrigation technology and what kind of crops you’re growing.”